The present invention relates to ballasting and electrical power transfer circuits. More particularly, this invention relates to a highly efficient, energy saving inverter ballast unit capable of operating multiple sets of lamps from any direct or alternating electric power source and to a novel multi-path leakage transformer used therein. The inverter ballast of the invention is particularly useful in operating gas discharge lamps, such as fluorescent lights.
Various types of electronic ballast systems for powering fluorescent lighting are known and presently used in industry and by the consumer. The converter-type electronic ballast is used to convert direct to alternating current in a portable battery set-up for powering relatively small fluorescent lamps of 8 to 25 watts, used, for example, in camping lanterns. For larger fluorescent lamps up to about 40 watts, such as for use on buses, trains, and airplanes, electronic converter ballasts are used which operate at so-called high frequencies of about 10,000 cycles, which are quite noisy. Since converter-type ballasts operate from a DC source, convenience, rather than efficiency of operation, is the primary consideration.
High-power inverter ballasts which operate at high frequencies from DC power sources are presently in use. These ballasts are used to ignite and maintain gas discharge lamps totalling, for instance, in the order of 20 kilowatts. However, in most known inverter ballasts, the inverter or power source is separate from the inductive-type ballast (when this type is used) for each lamp. While the efficiency of the above-described system can be increased by increasing the frequency, since increased frequency increases lamp efficiency and, therefore, light output, thus the final efficiency levels attained are considerably lower, because of losses in the separate ballast coils, than the levels approached by this invention.
Lastly, the standard inverter ballast used for home fluorescent lighting operates from either the normal 50/60 Hz AC or, in some cases, from a DC utility line, to produce, rather inefficiently, a given quantity of light.
More recent ballast systems have a dimming means by which the lamp light output may be reduced and, accordingly, power consumption may be decreased in some proportion. Such dimming means may consist of either a switch which connects different tap windings within a standard ballast coil, or an electronic SCR control which, when connected to the ballast, reduces the power supplied to the lamp (or lamps). The present invention, in contrast to the above, has an inherent dimming capability which permits the inverter ballast to vary continuously the lamp light output and reduce linearly, in a direct proportion, energy input into the device. Because of these features, the energy savings of this invention are considerably and dramatically higher than presently available dimmers for fluorescent lamps.